Stop Putting Mechanics in Damage Formulas

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MechanicsInsideDamageFormulas Example1 No.png

Every other RPG Maker MV/MZ battle-mechanics-loving user has seen this article on RPG Maker Web. It teaches you how to manipulate the damage formula to add in more complexity to skills and items. While most of what the article teaches is okay, the parts where it teaches you how to add mechanics to it aren't because they can conflict heavily with how your game is supposed to operate when the time comes. Don't worry, even I fell prey to this early on in the RPG Maker MV lifecycle.

Why do I say that?

That's because the damage formulas should be reserved for damage calculations only. While damage calculations typically occur during battle and/or processing of the effects, they also occur when a skill or item is being evaluated by the A.I. to determine if it's the right skill to use, too. Let's take a look at what happens when mechanics are placed in damage formulas.

Yanfly.png This is an article written by Yanfly.

A Brand New Project

Let's create a brand new project to show off the controlled aspects of this problem.

MechanicsInsideDamageFormulas BlankProject.png

The above screenshot is to show you that there are no plugins installed. This is to prove that there is no outside plugin influence to cause some of the problems occurring in what will be shown below.

Special Skills

Using the examples found in the article above, we'll have the following effects made for 4 different skills:

Power Strike:

MechanicsInsideDamageFormulas Example1.png

a.addBuff(2, 5); a.atk * 4 - b.def * 2

This is a skill that gives the user an ATK buff for 5 turns.

Risk Taker:

MechanicsInsideDamageFormulas Example2.png

a.addDebuff(3, 5); a.atk * 4 - b.def * 2

This is a skill that gives the user an DEF debuff for 5 turns.


MechanicsInsideDamageFormulas Example3.png

a.gainHp(Math.round(-a.hp * 0.5)); a.atk * 4 - b.def * 2

This is a skill that causes the user to lose 50% of their HP upon usage.


MechanicsInsideDamageFormulas Example4.png

a.setMp(0); a.atk * 4 - b.def * 2

This is a skill that causes the user to lose all MP (brings it to 0) upon usage.

The Berserker

MechanicsInsideDamageFormulas Berserker.png

Now, let's create a Berserker class! The Berserker class will be a standard class. It will have the four skills we've just made. It also has the trait: Auto Battle.

Why are we using Auto Battle? It's because it's one of the few ways RPG Maker utilizes the evaluation function for damage formulas.

Let's also assign the class to Harold.

MechanicsInsideDamageFormulas Harold.png

He seems fitting for the Berserker type, right?

Now that everything is ready, it's time to go over and do a battle test!

Witnessing the Problem

MechanicsInsideDamageFormulas Troops.png

Let's head over to the Troops tab in the Database. Pick any of them. I'm picking the first one since it's the most convenient.

Note that in the screenshot above, there are no Troop events to cause anything special from happening.

With that in mind, let's hit the Battle Test button and start a playtest.

Turn 1

MechanicsInsideDamageFormulas Turn1.png

On turn one, without doing anything at all, you'll see that Harold's HP is at 25% meaning his HP got halved TWICE, has his ATK buffed TWICE, has his DEF debuffed TWICE, and MP at 0.

Just what on earth happened? And why twice? I'll explain:


MechanicsInsideDamageFormulas Evaluate.png

The above two functions are the "culprit" to why this happens. I say "culprit" in quotes because it's not really a culprit. It's doing what it's supposed to be doing: its job of calculating the damage formula. It's not at fault that we, the game devs, decided to put game mechanics inside the damage formulas.

But why did it calculate without the actions being performed though?

That's because for some cases, like the A.I. for Auto Battle, all of a battler's available actions have to be evaluated in order to determine the optimal action to perform for battle. RPG Maker's A.I. is simplistic, find the largest number, go with the skill that produces the largest number. However, because we put mechanics in them, each time the calculations are made, the mechanics are also being performed.

Why did it happen TWICE though? Let's look back at the troops page:

MechanicsInsideDamageFormulas Troops.png

There are two enemies there.

The A.I. would evaluate each available skill for each available enemy. This means if there are two enemies, the skills are evaluated twice each. And this will happen each turn. If there are 8 enemies, the skills will be evaluated 8 times each. This means that the self-HP halving skill would occur 8 times over had there been a full enemy party.

Let's see what happens on turn 1 with 8 enemies instead.

MechanicsInsideDamageFormulas Turn1 8 Enemies.png

Poor Harold now starts battles with only 2 HP. Geez...

This problem is not exclusive to just Auto-Battlers either. Auto-Battlers just happen to be the easiest way to show the problem. This problem happens each and every time evaluations are made to determine the proper skill to use via A.I.

How To Fix It

There's a couple of ways to fix this. However, let's talk about the way to NOT fix it first.

How to NOT Fix it

MechanicsInsideDamageFormulas CodeNotFix.png

Some of you may be wondering if we can fix the code that does the evaluation (so that way, you guys can just leave your skills as is without having to redo them).

The answer is yes and no, but a hard leaning on no.

We could change up the code so that the evaluations that occur only happen to temporary clones of the user and potential candidates. That way, the temporary clones will disappear with any of the mechanical changes made to them. However, this can still trigger troop event pages, meaning even if an action didn't happen, the battle can potentially treat it as if it did.

Furthermore, mechanical changes to switches and variables cannot be reversed via cloning either. The same goes for any kind of common event calls an action make do if it was done via damage formula.

No matter how you look at it, you'll do more work trying to work around this than making your skill properly.

How to Properly Fix it

So how do we make the skill properly?

MechanicsInsideDamageFormulas CommonEvent.png

Do it by Common Event or use plugins that perform the mechanical changes OUTSIDE of the damage calculation portion of the skill. Assign these Common Events to the skill or item's Effects list.

The other solution is plugins:

If you are using RPG Maker MV, these plugins let you do that:

If you are using RPG Maker MZ, you can use this to do the same:


The biggest conclusion I can draw from this is what I've said earlier:

"Damage formulas should be reserved for damage calculations only."

This is because when mechanics get intertwined with it, anything that uses the damage formula's calculations will also cause the game suffer from it. The game definitely uses damage formulas outside the scope of plugins as you can see in the demonstration shown above in a vanilla RPG Maker project. This problem is not exclusive to just RPG Maker MV. It also happens in RPG Maker VX Ace and RPG Maker MZ, too. You don't see it happening in RPG Maker 2003, XP, or VX because those don't allow game devs to insert their own damage formulas.

Instead, separate your mechanics by putting them inside Common Events and/or using plugins to properly give them a suitable timing to apply the said mechanics. It's a shame that there aren't more ways to do cool things with skills with just the editor by itself, but the damage formula selection box is not the way to do it.

This is a problem that even I fell victim to before, but that's exactly why I wrote this article so that you guys don't have the same problems.